(1) Field of the Invention
This invention relates to a process for preparing porous, spherical cellulose particles.
(2) Description of the Prior Art
Various methods of separating and purifying substances have been developed with the progress in the field of biochemistry. The currently used methods as above include ion-exchange chromatography, gel filtration, affinity chromatography, and the like. Known materials used in the aforesaid methods include dextran, agarose, polyacrylamide, cellulose, and the like. Many attempts have been made by use of the aforesaid materials so that their properties as a gel filtering material or ion exchanger may be fully exhibited. A preferable form as the gel filtering material is a sphere from the standpoints of separation property, flow rate and the like.
Few practical applications of cellulose to the gel filtering material are known at present, but attempts on the preparation of spherical cellulose particles have been made so far. For example, a process for preparing cellulose particles from a viscose, or a cuprammonium solution, in which cellulose is dissolved, is disclosed in Japanese patent laid-open specification Nos. 60753/1973, 60754/1973, and 5361/1976, and Japanese patent published specification No. 11237/1977. On the other hand, Japanese patent laid-open specification No. 7759/1978 discloses a process for preparing spherical cellulose particles from cellulose acetate.
The process according to Japanese patent laid-open specification No. 7759/1978 is so improved as to make it possible to obtain real spherical cellulose particles having excellent properties as the gel filtering material. The aforesaid process is such that a cellulose triacetate solution dissolved in a chlorinated hydrocarbon solvent or in a mixed solvent consisting mainly thereof as a stock solution is added dropwise into an aqueous medium with stirring to form suspended particles, and that the aqueous medium containing the suspended particles is heated to evaporate the solvent and subsequently to form cellulose organic ester spherical particles followed by saponification thereof. The gel filtering material is often used for the so-called desalting, in which a polymeric substance such as protein is separated from a salt such as sodium chloride, urea, ammonium sulfate, or the like. The desalting has been applied on an industrial scale, in which desirable properties as the gel filtering material require that many samples can be separated fast with high purity. In order to satisfy the aforesaid properties, some difference is needed between an elution volume of protein and that of salt. In case that such a gel that has a small difference between elution volume of protein and that of salt is used for the treatment of much quantity of sample, the separation ability of the gel is insufficient and it causes poor purity of eluates, consequently, the gel is hard to be used for industrial scale.